In recent years, electric drive vehicles such as an electric vehicle (EV), a plug-in hybrid electric vehicle (PHEV) and the like become popular. Also, various kinds of power conditioners for a V2H (Vehicle to Home) system have been proposed for the purpose of using a vehicle storage battery equipped on the electric drive vehicle as a household power supply.
The power conditioner is generally constituted by a bidirectional DC/AC inverter (hereinafter, referred to as a bidirectional inverter) which is connected to the commercial power system and performs the linkage operation, and a bidirectional DC/DC converter to be connected to the vehicle storage battery equipped on the electric drive vehicle. The bidirectional DC/DC converter is required to have a function of electric power conversion from a battery voltage of the vehicle storage battery into a DC voltage required as an input of the bidirectional inverter, and a function of conversion from a DC voltage output from the bidirectional inverter into a charge voltage of the vehicle storage battery.
Conventionally, the bidirectional DC/DC converter includes a first conversion circuit including switching elements connected in a half-bridge manner and a voltage doubler rectifier circuit, and a second conversion circuit including switching elements connected in a full bridge manner. Power transfer between the first conversion circuit and the second conversion circuit is performed through a transformer, and the first conversion circuit and the second conversion circuit are electrically insulated by the transformer (for example, refer to JP 2011-120370 A).
The power conditioner for the V2H system is to be connected between the commercial power system and the electric drive vehicle, and controls charging and discharging operations between the vehicle storage battery and the commercial power system. The power conditioner is generally constituted by the bidirectional inverter which is to be connected to the commercial power system and performs the linkage operation, and the bidirectional DC/DC converter to be connected to the vehicle storage battery equipped on the electric drive vehicle.
The bidirectional DC/DC converter is required to have a function of performing electric power conversion from various battery voltages (DC150V to 450V) of the vehicle storage batteries into the DC voltages required as input of the bidirectional inverters in accordance with the battery voltage of a connected vehicle storage battery to be discharged. If a specification of an AC output of the bidirectional inverter is AC200V, the DC voltage required as an input of the bidirectional inverter is about DC300V to 400V. Also, if the specification of the AC output of the bidirectional inverter is AC 100V, the DC voltage required as an input of the bidirectional inverter is about DC 150V to 200V.
A voltage of the commercial power system to be connected to the bidirectional inverter is AC200V or AC100V. Accordingly, the bidirectional DC/DC converter is also required, for a charging operation of the vehicle storage battery, to have a function of performing electric power conversion from a DC voltage output from the bidirectional inverter connected to the commercial power system of AC200V or AC100V into any of the charge voltages of the vehicle storage batteries.
Accordingly, the bidirectional DC/DC converter is required to have a wide input voltage range and a wide output voltage range so as to be used for the various battery voltages of the vehicle storage batteries and various system voltages of the commercial power supplies. That is, such a bidirectional DC/DC converter is required that has a function of bidirectionally boosting and stepping down voltages in accordance with voltages selected from a wide range of battery voltages of vehicle storage batteries and a wide range of system voltages of commercial power supplies.